Phytoecdysteroid treatment increases fiber size and PI3k‐Akt signaling in aged skeletal muscle

Abstract

Protein synthesis through the PI3k‐Akt pathway is reduced in aged skeletal muscle, leading to a decrease in fiber size and number. Phytoecdysteroids, in particular 20‐hydroxyecdysone (20E), from the plant Ajuga turkestanica increases protein synthesis in C2C12 skeletal muscle cells and muscle strength in young rats. The objective of this study was to determine if an extract from A. turkestanica (ATE), enriched in phytoecdysteroids, affects muscle fiber size and PI3k‐Akt signaling in skeletal muscle of aged mice. Aged male C57BL/6 mice (20 mo) received ATE, 20E, or vehicle (CT) only for 28 days. H&E staining revealed 41% and 30% larger fiber cross‐sectional area (CSA) in the triceps brachii (p=0.014) and plantaris (p=0.018) muscles of 20E‐treated sedentary mice, respectively, compared to CT. ATE treatment resulted in larger, but non‐significant differences in CSA of the triceps brachii (26%; p=0.088) and plantaris (8%; p=0.497) muscles, compared to CT. Western blotting performed on gastrocnemius muscles showed a significant increase in phosphorylation of Akt in 20E‐treated sedentary aged skeletal muscle, compared to CT (p=0.013). In conclusion, these data suggest that 20E rescues the loss of muscle fiber size and increases activation of the PI3k‐Akt pathway in sedentary aged skeletal muscle. Supported in part by a USDA Kannapolis Scholars Fellowship.